The invention relates to apparatus for accumulating stacks of paper sheets and the like. More particularly, the invention relates to improvements in apparatus for accumulating stacks from sheets which are made of paper, plastic material, metallic foil, cardboard or the like and wherein a stream of advancing sheets is continuously converted into a succession of stacks, especially stacks which are assembled of large sheets.
It is known to convert a continuous stream of successive non-overlapping or partially overlapping sheets of paper or the like into a succession of stacks each of which contains a predetermined number of fully overlapping sheets. Such apparatus can be used in a production line for the making of exercise books, steno pads and similar stationery products. As a rule, the stacks are accumulated on a table which is movable between a stack accumulating or collecting position and a second position preparatory to transfer of a fully grown stack to a removing device, such as a set of belt conveyors. The table is movable from a higher level to a plurality of lower levels at the rate at which the height of the growing stack thereon increases. The sheets which are delivered while the table transfers a fully grown stack to the removing device are gathered by a carrier so as to avoid the need for a stoppage of the delivery of sheets to the stacking or gathering station. The sheets can be advanced from a cross cutter which severs a single running web of paper or other sheet material at regular intervals or which is designed to sever at regular intervals two or more overlapping webs of sheet material so that the overlapping webs are converted into a succession of composite sheets each of which comprises two or more individual or discrete sheets, depending upon the number of overlapping webs.
It is desirable and advantageous to transport a fully grown stack on the table away from the gathering station in such a way that the next-following sheets are not damaged during accumulation into a pile of overlapping sheets preparatory to their transfer onto the evacuated table as well as that the delivery of sheets can proceed without any interruptions. The sheets are most likely to be defaced and/or otherwise damaged at the top of the fully grown stack as well as the bottom of a growing stack.
Apparatus of the above outlined character are known and are in actual use in a variety of forms. Reference may be had, for example, to British Pat. No. 929,540 which discloses a vertically adjustable table for accumulation of a growing stack. The table is lowered at the rate at which the stack thereon grows so as to ensure that the top of the growing stack is in an optimum position for reception of the oncoming sheet. When the table accumulates a preselected number of sheets, a separating device is caused to enter the gathering station and to intercept the next-following sheets as well as to support the intercepted sheets during transfer of the fully grown stack onto the removing device. Such transfer takes place by moving the entire table from its operative position at the gathering station to a second position in which the fully grown stack thereon is transferred onto the removing device. The patent proposes to employ a supporting strap which is caused to extend beneath the gathering station while the table and the fully grown stack on it are being transferred to the removing device In other words, the strap constitutes a temporary support or carrier for the growing stack. A drawback of such proposal is that the supporting surface of the strap is not overly stable because its stability depends upon the tensioning of the strap and on the weight of the sheets thereon. This can entail undesirable changes in the configuration of the growing stack so that the fully grown stack cannot be properly manipulated in the next-following treating unit, such as a packing machine. Moreover, all movements between the table and the stacks as well as between neighboring (fully grown and growing) stacks are affected by friction.